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NEW YORK – Tests have confirmed there was heroin in at least some of the scores of plastic packets in the New York City apartment where Philip Seymour Hoffman was found dead, a law enforcement official said, and authorities are working to determine whether the drug was mixed or tainted with anything else.

Medical examiners have not yet made an official determination of the cause of the 46-year-old actor’s death, but police have been investigating it as a suspected overdose. Hoffman was found in a bathroom with a syringe in his arm, law enforcement officials have said.

A few details began to sketch a picture of Hoffman’s final day and the circumstances in which he was found in his apartment in Manhattan’s Greenwich Village on Sunday. And questions have swirled about whether Hoffman’s death could be linked to a potent blend of heroin and synthetic morphine that has been tied to deaths elsewhere, though as yet there are no official findings pointing to that scenario.

“The direction of the investigation is going to depend, in large part, on the findings of the medical examiner and the findings of the lab tests,” chief police spokesman Stephen Davis said.

An autopsy began Monday, but results weren’t expected until at least Tuesday, the city medical examiners’ office said.

A friend had spoken to him by phone around 9 p.m. Saturday, in the last contact investigators are aware of anyone having with him, a law enforcement official said. The official said the actor’s door was double-locked when his body was found around 11:30 a.m. the next day by the same friend and Hoffman’s assistant.

In the apartment were at least four dozen small packets variously stamped with the ace of hearts and others with the ace of spades, two law enforcement officials said Monday. Tests of samples showed heroin in each type, one of the officials said.

Stamps are common as a form of drug-world branding, and authorities make note of the ones they encounter, though they’re hardly trademarks – different producers might use the same symbol. It wasn’t immediately clear whether the ace of hearts and ace of spades stamps could lead investigators to any clues about the source of the items found in Hoffman’s apartment.

Concern has risen around the region in recent months about fentanyl, a synthetic morphine substitute roughly 100 times more powerful than morphine, being mixed with or substituted for heroin. In western Pennsylvania, 22 people died within a week last month from suspected overdoses of heroin and fentanyl, Attorney General Kathleen Kane said last week; at least a half-dozen suspected dealers have been charged there.

On New York’s Long Island, the Nassau County medical examiner’s office said Friday it was investigating several deaths initially assumed to be heroin overdoses but later found to have involved fentanyl being sold in packets stamped “24K.”

In New York City, a fentanyl-heroin blend cropped up recently in a case against a man charged last month with running a sizeable heroin and cocaine ring. In one of various alleged deals, he sold a 200-gram package of powder that later tested positive for both heroin and fentanyl, a prosecutor’s office spokeswoman said Monday.